A wide variety of machines for paving and compacting paving materials such as asphalt have been used for decades. The term “asphalt” is used broadly herein in reference to the class of paving materials consisting of aggregate mixed with one or more viscous materials such as petroleum-derived asphalt, other definitions for “asphalt” notwithstanding. A conventional approach for paving a surface such as a road or parking lot is to distribute hot paving material onto a prepared bed with a paving machine, then follow the paving machine with one or more compacting machines to compact the material to a desired density and obtain an acceptable surface finish. Most commonly, the compacting process is performed with double drum compacting machines, having a front drum and a back drum, which serve to propel the machine and compact the asphalt to a suitable state via the weight of the compacting machine, often in cooperation with drum vibrating apparatuses. Completing compaction can often require multiple passes across the asphalt mat with the compacting machine.
A typical system for paving a work area such as a parking lot or road can include numerous different machines. Supply machines such as haul trucks may be used to deliver paving material for distribution and compaction on a work surface. The paving machines may be supplied directly from the haul trucks, or from material transfer vehicles. The paving machines typically distribute paving material and perform a preliminary compaction of a “mat” of paving material with a screed mounted at a back end of the paving machine. In many systems, the paving machine is followed relatively closely by a compacting machine known in the art as a breakdown roller. Another compacting machine known as an intermediate roller often follows the breakdown roller, and a final finish roller may follow behind the intermediate roller in some systems. Various factors can affect the efficiency and success of a paving job, such as operator experience with the various machines, environmental conditions and temperature of the paving material at different stages of the paving process. Working paving material under optimum temperature conditions has long been recognized as important, but has before now been difficult to ensure and verify without manual measurements by support personnel.
Paving material is typically obtained at a relatively high temperature at an asphalt plant. Depending in part upon the distance a supply machine has to travel to reach a work site, traffic, ambient temperature, etc., the asphalt can cool somewhat prior to delivery. Progress of the paving machines and compacting machines can also vary, and haul trucks may have to wait to offload the paving material if paving has slowed. The manner in which paving material is delivered to a paving machine can also vary among systems, e.g. via a material transfer vehicle or “MTV” versus direct delivery from a haul truck. Due to the variables which can affect the timing of the various events in a paving process, a temperature of the paving material when it eventually reaches the paving machine can be at least somewhat unpredictable.
Once transferred into a paving machine, paving material will tend to cool further, prior to being distributed onto a work surface. The extent of cooling, once within the paving machine, can vary depending on the temperature of paving material at delivery, environmental factors, proper versus improper operation of the paving machine, etc. In some instances, paving material may segregate within a paving machine, and thus relatively cooler and relatively warmer pockets of material within the machine may exist, leading to unexpected temperature gradients in the paving material once distributed on the work surface. When paving material is finally discharged and distributed by the paving machine, treated via its screed, and ready to be compacted by the various compacting machines, its temperature can vary significantly from an expected temperature, and may even be non-uniform from one paved region to the next due to unintended segregation or poor mixing. As alluded to above, being able to work paving material under certain conditions such as optimum temperature can often be of paramount importance.
For example, depending upon the particular mix of paving material, it may have a temperature range known in the art as the “tender zone” where attempted compacting is unlikely to succeed. When paving material temperature is in the tender zone it may be prone to shoving and, as a result, there may be a “wave” in front of the compacting machine drum. It is well known in the paving arts that successful compaction may take place in one of potentially multiple “optimal temperature zones” when the paving material temperature is either above the tender zone or below the tender zone but above a minimum temperature. Ideally, breakdown rollers, mentioned above, follow the paving machine closely enough that they compact paving material prior to its cooling to the tender zone or the minimum temperature. Intermediate rollers typically follow sufficiently far behind the breakdown roller that the paving material has cooled below the tender zone by the time the intermediate roller reaches a particular stretch of paving material. It is also typically desirable to employ the finish roller prior to paving material cooling to below a minimum temperature at which the paving material becomes too hard.
Sticky, viscous properties of hot paving material can cause it to adhere to paving and compacting equipment where relatively cool machine components come into contact with the paving material. This tendency for hot paving material to stick to machine surfaces is generally a function of the heat transfer out of the paving material. The paving material may congeal and increase in viscosity where it is cooled by contact with machine surfaces. The greater the difference in temperature between the paving material and machine surfaces, the greater the tendency for paving material to stick.
As paving material is laid down by a paver, a component of the paver known as a screed is typically used to prepare the paving material for compacting. Screeds commonly include a metallic implement having a surface which slides across a pile of paving material deposited on a work surface to level and slightly compact the paving material in anticipation of further working by a compacting machine. The efficacy of the screed and ultimately quality of the paving job may be affected where paving material adheres to the screed instead of smoothly slipping past the screed surfaces. In other words, paving material stuck to the screed can affect the ability of the screed to provide a paving material mat suitable for finishing with a compacting machine. Irregularities in the paving material mat laid down in advance of the compacting machine(s) can result in unevenness in the later compacted surface.
In addition to the challenges to successfully paving in the first place, many jurisdictions now mandate logging data relating to paving material temperature and machine activities during a paving operation. Records of such operations at a paving site allow paving contractors to establish that paving was performed within specifications, and are commonly related to contract validation and bonuses as well as predictive and forensic aspects of construction. Standard procedure for this type of data logging has heretofore relied principally on manual observation and recording of the temperature of paving material while working a particular area.
One way of monitoring pavement temperature for compaction operations is disclosed in U.S. Pat. No. 6,749,364, entitled “Temperature Sensing for Controlling Paving and Compaction Operations.” U.S. Pat. No. 6,749,364 discloses a pavement temperature monitoring system on a paver vehicle with a temperature sensor and a display device which can receive an electrical signal sent by the temperature sensor and generate a graphical image corresponding to the signal.
Accordingly, what is needed is a device and method to determine, communicate, and display the temperature of paving material in conjunction with a predictive temperature and positional model to operators of paving and compacting machines.